This invention relates to blasting mats which are constructed from resilient sections of used tires.
Blasting mats constructed from sections of used vehicle tires are known, an example of such blasting mat being described in Canadian Pat. No. 753,870, granted to Lionel Belanger on Mar. 7, 1967. When excavating to permit construction in rocky areas, blasting is often required to loosen or fragment the substrata, before digging may take place. After explosive material has been planted, it is desirable, before detonation, to provide a means which will muffle or dampen the upward thrust of the exploding material. The provision of such a dampening means causes the forces of the explosion to radiate outwardly and downwardly where they are most useful. Additionally, such a means reduces or eliminates the scattering of debris from the explosion site. Blasting mats have therefore been used to improve the effectiveness of blasting, and to protect workers, machinery, buildings or the like, located at close proximity, from the hazards normally associated with unprotected blasting.
It is desirable that a blasting mat be transportable, and be made up of strong, resilient and inexpensive sections which are easy to assemble. The sections are desirably held together in fixed proximity each to the other by sufficiently strong means so that the mat may withstand the impact forces of repeated explosions.
A major disadvantage with the Belanger blasting mat, illustrated and described in Canadian Pat. No. 753,870, and other known blasting mats, arises due to the nature of the sections used in construction. They are sections of used tire halves. The tire halves normally have been cut into three or more sections which have been provided with holes near the ends of each section so that the sections may be threaded into a mat structure with steel cable or the like. During blasting operations the sections tend to pull away from the cables, and there tends to be tearing in the ends of the sections in a direction tangential to the circumferential arc of the tire section at a point located at the end of the tire section. The Belanger arrangement of tire sections is relatively complex, and the expense of cutting tires into sections is another disadvantage of the Belanger proposal.
While used tires which are suitable for incorporation into a blasting mat may have had external features, such as the tread portions, worn away to some extent, the internal features, such as internal cord structures, normally remain intact. At least some of the internal cords are oriented circumferentially around the axis of rotation of the tire. For the purposes of this specification, a vehicle tire is presumed to have an axis of rotation which is the straight line about which the tire would rotate if it were operationally mounted on a vehicle. If these cords are cut when each tire half is sectioned along lines which extend radially through the tire, as proposed by Belanger and others, then during a blasting operation, the forces on the tire section are such that the cables holding the mat together tend to pull out of the tire sections in a direction parallel or nearly parallel to the internal cords which have been severed. The ability of each individual section to withstand these stresses, and the strength of the mat as a whole, is accordingly diminished by the severing of the internal cords in the tires.